Lecture 13 More informal fallacies: - Appeal to Ignorance - Slippery Slope - False Dichotomy - Alternate Description - Composition/Division

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1 Lecture 13 More informal fallacies: - Appeal to Ignorance - Slippery Slope - False Dichotomy - Alternate Description - Composition/Division Appeal to Ignorance Committed when the arguer claims that a lack of evidence for some claim constitutes evidence for that claim s negation. Nobody has ever proved that God does not exist, so God must exist. Nobody has ever proved that ESP is true, so it must be false. I ve looked all over this room, and I can t find my keys, so they must not be here. Slippery Slope the arguer claims that his position must be preferred because the only other position will lead to a chain of events leading to undesirable consequences. It is a fallacy if in fact the chain of events is not likely to occur. We should outlaw pornography. The continued manufacture of this material will lead to an increase in crimes such as rape and incest. This will gradually erode the moral fabric of society, resulting in increased crimes of all sorts. Soon, we will be facing the complete collapse of law and order, and perhaps the end of civilization. Attempts to outlaw pornography should be abandoned. If pornography is outlawed, then this will open the door to censorship of newspapers and magazines. Then we will see textbooks and university curricula censored as well. Then the government will be in the business of maintaining complete mind control over us all.

2 We should pay to have the hole in the dam fixed immediately. If we do not, then the water levels will continue to rise, overflowing the banks of the river. Eventually, the entire valley will be flooded, and the town will be under water. Surely we can t allow this to happen. False Dichotomy The fallacy of false dichotomy is committed when the arguer claims that his conclusion is one of only two options, when in fact there are other possibilities. The arguer then goes on to show that the 'only other option' is clearly outrageous, and so his preferred conclusion must be embraced. Either you let me go to the Family Values Tour, or I'll be miserable for the rest of my life. I know you don't want me to be miserable for the rest of my life, so you should let me go to the concert. Either you use Speed Stick deodorant, or you will stink to high heaven. You don't want to stink, so you better buy Speed Stick. Either I keep smoking, or I'll get fat. I don't want to get fat, so I better keep smoking. Either we keep Charles Manson in jail, or we release him, thus risking murder, carnage, and mayhem. We don't want murder, carnage, or mayhem, so we had better keep him in jail.

3 Comparison between Slippery Slope and False Dichotomy Both essentially have the form of a disjunctive syllogism. (Which is a valid form of inference!) Slippery Slope 1. A v B 2. ~B 3. A False Dichotomy 1. A v B 2. ~B 3. A i. B C ii. C D iii. ~D iv. ~B i. B C ii. C D iii. ~D iv. ~B Alternate Description the arguer responds to an opponent s argument by providing an alternate description of an object or event, and implying that under the new description the opponent s argument is flawed. It is a fallacy if the original description is more appropriate. My ex-wife got all bent out of shape last week because I took our eight-year-old son to a topless bar. She said I was being a bad influence. But the courts said she has to let me spend time with my son, and I was just trying to spend time with him! How can spending time with your loving father be a bad influence? My client is not a drug dealer. He is simply trying to provide for his family. How can the court put someone in jail for trying to provide for his family??!! As for the accusations that the administration has been harassing student run organizations, they are groundless. We have been actively enforcing the standards that the student government itself established for the operation of these organizations. For example, we shut down Classical Notes because they were forcing their employees to work through finals week.

4 Composition/Division one mis-attributes properties of the whole to the parts (division), or properties of parts to the whole (composition). How can you say that my paper is poorly written? Show me one sentence here that is ungrammatical or unclear! American families have 2.6 children. The Smiths are an American family, so they must have 2.6 children. The United States uses many times more energy per year than does Denmark. Why are you Americans so wasteful? You should put your seat belt on even though you are only going to the store. Statistics show that most accidents occur within 10 miles of home, and so it is in fact more dangerous driving near home than elsewhere. The Balboa Suspension Bridge was constructed using the strongest steel available, so the bridge must be extremely strong.

5 Either this key fits the front door or it s the wrong key. But it clearly doesn t fit. It s much too large. Therefore, it s the wrong key. No one has ever proved that smoking small amounts of marijuana over long periods of time is harmful. We can therefore conclude that this practice is safe. Gerda Reith is convinced that superstition can be a positive force. 'It gives you a sense of control by making you think you can work out what's going to happen next,' she says. 'And it also makes you feel lucky. And to take a risk or to enter into a chancy situation, you really have to believe in your own luck. In that sense, it's a very useful way of thinking, because the alternative is fatalism, which is to say, "Oh, there's nothing I can do." At least superstition makes people do things.' [Joe McCarthy] announced that he had penetrated 'Truman's iron curtain of secrecy' and that he proposed forthwith to present 81 cases Cases of exactly what? 'I am only giving the Senate,' he said, 'cases in which it is clear there is a definite Communist connection persons whom I consider to be Communists in the State Department.' Of Case 40, he said, 'I do not have much information on this except the general statement of the agency that there is nothing in the files to disprove his Communist connections.' Mr. Cohen thinks marijuana should be legalized, but does he realize the kind of effects drugs have on kids? Not only are many drugs dangerously addictive, needle use among drug addicts often leads to the propagation of the AIDS virus. Why don t you support the death penalty? Do you want hardened and dangerous criminals wandering the streets?